A junior representative for South Australian National Football League (SANFL) club Central District as well as playing cricket, Lehmann left school at the age of 16 to work on the assembly line of Holden car manufacturers in Elizabeth, South Australia. He declined selection to the first intake of the newly formed Australian Cricket Academy, a full-time cricket centre, citing his enjoyment of the factory life. Lehmann entered the first-class scene as a 17-year-old in the 1987/88 season for South Australia, playing one match against Victoria at the Melbourne Cricket Ground after both Tim May and Peter Sleep were called into the national team. After making 10, Lehmann was omitted upon their return and did not play any further part in the season. In 1988/89, South Australia were at the bottom of the ladder, when coach Barry Richards called Lehmann into the team, playing against Western Australia at the WACA. Lehmann remembered little of the match; after being struck in the right temple by a Bruce Reid bouncer, he was knocked unconscious and temporarily ceased breathing. Lehmann made his mark in the following match against New South Wales Blues at Adelaide Oval, reaching 50, but the innings was marred by the manner in which it was ended. Going for a quick single, Lehmann collided with bowler Geoff Lawson and was run out after falling over. However, Richards and South Australian captain David Hookes claimed that Lawson had tripped Lehmann, leading to a confrontation between the two teams.

In 1989/90, Lehm